ABSTRACT
Large scale grain production in northern Kazakhstan began in mid-1950s, and it involved conversion of grasslands into cropland ecosystems. From the very beginning, the recommendation was to grow spring small grains, primarily spring wheat, continuously with summer fallow once every 5 years. This recommendation was based mostly on the Canadian practice of alternate summer fallowwheat in dryland agriculture. Long-term data obtained on black soils have shown that frequent summer fallowing reduces total grain production from cropland and leads to rapid losses of soil organic matter (SOM). Long-term comparative data obtained for three crop management practices (simple, common and best) in Kazakhstan supported the conclusion that summer fallow is not justified for any of these technologies. Summer fallow, however, leads to a better supply of NO3-N for plant growth and also to a better grain baking quality. Thus, the objective of this chapter is to describe the long-term effects of summer fallow on yield of spring grain crops, total productivity, and environment quality in black soils of northern Kazakhstan. Spring wheat is sown in the second half of May and harvested between mid-August and mid-September in northern Kazakhstan. Thus, the summer fallow period lasts 20-21 months. For a long period since development of new lands in mid-1950s, summer fallow was deemed necessary for the success of dryland farming. The only debatable point was the frequency of incorporating fallow in the rotation cycle. Canadian practice of alternate fallow-wheat was found to be unacceptable under conditions of Kazakhstan from the very beginning. In the 1960s, summer fallow was recommended to occupy 25% of the crop rotation cycle. In the 1970s, the duration of fallow was reduced to only 20%, and later on in 1980s the duration was further reduced to 16.7%. In other words, summer fallow was recommended once in four, five or six years of the rotation cycle during 1960s, 1970s and 1980s, respectively.
